。
Her eyes sparkled when they caught the light of the room.
Literal
Eye [subject-が] room [possessive-の] light [object-を] reflected-[when-とき], her [possessive-の] eye [topic-は] sparkled.
Two occurrences of 目 with different marking: the first, inside the temporal subordinate clause (...ときに), uses が because it's a new subject of the embedded clause; the second, in the main clause, uses は because the topic of the overall sentence is 'her eyes.' This が/は split — new referent in the subordinate clause, topic in the main clause — is a standard pattern. 輝く ('to shine, sparkle') is a common verb for eyes, stars, and faces lighting up.